Microsphere solid metal lubricant



Dec. 22, 1970 I R. SANTT 3,549,531 mIcRdsPaERE so w METAL LUBRICANT 7Original Filed Feb. 24. 1964 lllvllllrl/ 41m 0440/ 55% 9 United StatesPatent 3,549,531 MICROSPHERE SOLID METAL LUBRICANT Ren Santt,Villefranche par Dun-sur-Meuse, Meuse, France, assignor to CentreNational de la Recherche Scientifique, Paris, France, a society ofFrance Continuation of application Ser. No. 346,881, Feb. 24, 1964. Thisapplication Feb. 27, 1967, Ser. No. 624,969 Claims priority, applicationFrance, Dec. 18, 1963,

rm. (:1. 610m 5/02 US. Cl. 25226 Claims ABSTRACT OF THE DISCLOSURE Solidmetal microsphere lubricants used between slidably engaged surfaces.

This application is a streamlined continuation of application Ser. No.346,881 filed Feb. 24, 1964 and now abandoned.

The present invention relates to the field of lubricants and moreparticularly to lubricants made from solid materials in the form ofmicroscopic particles.

The advent of commercially available particulated materials of uniformlyspherical shape, and having diameters of the order of microns, has ledto many new applications which take advantage of their unusualproperties. They have come to be used as filters for aircraft panels, asfloating protective layers on oil reservoirs, as packing materials forfragile objects, etc. These materials have been found to be quite hard,mainly because their shape prevents their being subjected to tangentialstresses, and extremely easy to handle since their solid nature ensuresthat they will not chemically or mechanically deteriorate theircontainers.

The present invention seeks to extend the range of uses of thesematerials to the lubricating field in which they have been discovered tohave several extremely valuable applications. In addition thesematerials present certain striking advantages over prior art lubricantsin that they are relatively insensitive to both wide variations oftemperature and the passage of time and they do not present thecontainment problems inherent in the use of liquid or amorphouslubricants. These materials have proven to have excellent lubricatingqualities, especially when used in combination with certaintemperature-insensitive liquids which have not been previously thoughtof as effective lubricants.

It is, therefore, an object of this invention to produce a lubricantwhich is relatively insensitive to wide variations in temperature andpressure and to the passage of time.

It is another object of this invention to produce a lubricant consistingat least in part of solid, spherical particles.

It is yet another object of this invention to achieve a lubricatingaction which is superior to that previously achieved by conventional,light-weight, liquid lubricants.

These and other objects, features and advantages will become morereadily apparent from the following description, when taken togetherwith the accompanying drawings, in which FIGS. 1 and 2 are graphsshowing the properties of the lubricants of the present invention incomparison with those of prior art lubricants.

The lubricants envisioned by the present invention are characterized bythe fact that the particles forming at least one ingredient thereof arein the form of hard spheres which are calibrated, that is to say sized,so as to be as uniform as possible in diametral size. This sizing isconducted with a view of obtaining spheres the diameter D of which iswithin the range of D Di These spheres have a diameter of less than 40micron and preferably less than 8 microns. It is preferred that thematerials constituting these particles be taken from the groupconsisting of iron, nickel, cobalt, tungsten, aluminum, or an alloy ofthe bronze type. Such spheres are commercially available in anon-calibrated state.

In order to calibrate them, one can have recourse to a sedimentation inthe gaseous phase, for example by a passage of the particles without theaid of secondary air in a vortex separator of the Walther or Bahcotypes, or by a sedimentation in an appropriate liquid medium.

According to another method, one could prepare the spheres bydecomposing the metal carbonyl of one of the above named materials, ifit exists.

As an example, and purely by way of illustration, one could produce thedesired iron spheres, for instance, by injecting the iron pentacarbonylin a current of ionized hydrogen, the latter being inert with respect tothe iron pentacarbonyl, at a temperature above C. The resultingdecomposition of the iron pentacarbonyl is followed by the condensationof the alloy around nuclei constituted by the hydrogen ions present. Thespheres obtained by this process result from the superposition ofsuccessive concentric layers of the alloy and are thus relativelyuniform in size. The resulting spheres are thus subjected to a firstcalibration at the very moment of their production.

Advantageously, one can complete the calibration by one of the methodsdescribed above.

Still by way of example such a process was carried out and it resultedin the production of a powder consisting of iron spheres havingdiameters which were uniform and of about tWo microns, having thefollowing chemical composition:

Percent Percent Carbon 0.6 Nitrogen 0.5 Oxygen 1.0 Iron 97.9

The hardness of these small spheres, expressed in D.P.N. units, was inthe neighborhood of 850, being notably superior to that of the hardeststeels.

Experimentation shows that the spherical particles thus produced areremarkably resistant to corrosion.

Because of the microscopic size of these particles their emplacementbetween the surfaces to be lubricated ofter requires special measures.In accordance with the invention, one can utilize, in order to achievethis emplacement, a suspension of the spheres in a volatile liquid, forexample alcohol, which evaporates very rapidly after the emplacementoperation with the result that only the spheres remain between thesurfaces to be lubricated.

With respect to the quantity of lubricant introduced between the rubbingsurfaces, it is preferred that there be just enough spheres to form asingle layer in which the spheres are in contact with each other.

In the preceding discussion, the lubricant produced according to thepresent invention consisted solely of the spherical particles describedabove. However, the present invention is also directed to lubricantswhich are prepared by mixing these particles with a binder constitutedby a substance which can be either a low density liquid or a viscoussubstance and which does not have any corrosive properties with respectto either the spherical particles or the surfaces to be lubricated.

The respective proportions of particles and binder are chosen so that,once the lubricant has been applied to the surfaces to be lubricated,the particles will present the single, continuous layer described above.

One could select, for the binder, a substance which itself has theproperties of a lubricant. Such a substance, which must be able toresist temperature and pressure variations without experiencing anexcessive change in its properties, can be in the form of a grease or anoil, either vegetable, mineral, or synthetic.

On can also select a binder material from among substances which do notthemselves necessarily have lubricating properties but which possessother properties, for example relative insensitivity to wide variationsin temperature and pressure or to other conditions, such as the presenceof an ionized medium.

By way of example, there could be mentioned liquids which are stable upto temperatures of 400 C. and which are moreover uninflammable. Suchliquids are usually chosen from the group consisting of chlorinatedbenzene, chlorinated diand polyphenylic derivatives, hexachlorobutadieneand others.

With reference to the binders which are insensitive to ionizedenvironments, diphenyl ether may be mentioned as an example. Otherbinders which could prove useful are constituted by silicones andpetroleum.

In order to give one example of the combinations described above, it hasbeen observed that a pair of rubbing surfaces could be lubricated byspherical particles to which petroleum has been added, the combinationof petroleum and spherical particles having been found to haveremarkable lubricating properties. In order to clearly point out thevalue of these properties reference will be made to FIG. 1 which showscurves indicating the operation of a rotating device which waslubricated by a different substance during each run.

The curves of FIG. 1 indicate the motor operating current versus timefor a motor driving a small speed reducer, the latter being the elementwhich was lubricated by the various materials. The speed reducer was ofthe SAGEM brand, type 1070, and was driven by an electric motor runningat 7750 rev/min.

Without any lubrication at all (point A) the speed reducer started at amotor current of 10 ma.; when lubricated with petroleum alone (point B)it also started at 10 ma., leading to the conclusion that the petroleumprovides no reduction of the friction in the speed reducer; lubricatedby a special oil (point C) the device started at 5 ma.

For the next test run, a lubricant representing one of the embodimentsof the present invention was used. It consisted solely of tinycalibrated spheres obtained from iron carbonyl, of the type described indetail above, and its use resulted in a motor starting current of 11 ma.(point D). The same motor current was obtained for a lubricantconsisting of a suspension of iron particles in alcohol, after thealcohol has had time to evaporate (point E on curve E). This increasewith time of curve B is probably due to a clogging of the tiny spheresin the bases of the reduction device gear teeth. The curve B, which hadan initial value of 2 ma. (point E represents the increase with time ofthe motor current as the alcohol evaporated.

The final experimental value, point F, represents the motor current whenlubrication is provided by a suspension of the above-described ironcarbonyl particles in petroleum of the same type as that used to obtainpoint B, such a combination having been described above. This current isof the order of 1 ma., or 5 times less than that obtained with a usualhigh-grade lubricating oil.

These results clearly show that the presence of iron carbonyl spheres ina petroleum medium gives to the combination lubricating properties whichare not possessed by petroleum alone.

The presence of the tiny spheres in lubricants applied between rubbingsurfaces eliminates all dangers of abrasion or gouging of one surface bythe other, the pheres playing the role of tiny balls which roll incontact with one another between the two surfaces to be lubricated andwhich not only prevent all seizing between the surfaces but are alsocapable of freeing units which had previously become seized.

Moreover, experiments have shown that the lubricants according to thepresent invention effect a constant polishing of the friction surfaces,thus continually improving their sliding characteristics. This leads toa continual reduction in both the heat generated by the sliding actionof the surfaces and their wear, all of which prevents the formation ofdeep fissures during operation. Further, the quality of the lubricationprovided by the lubricants of the present invention does not deterioratewith time.

In order to establish the verity of this latter assertion, a group oftests were run to determine the friction torque experienced by a devicerotating in a ball bearing unit which was successively lubricated byvarious substances. The results of these tests are shown in FIG. 2,wherein the curves illustrate the characteristic of friction torqueversus time obtained by the use of various lubricants.

Curve I represents the friction torque versus time characteristic whenthe device is run without any lubricant while curve II represents thecase where a few drops of petroleum have been added. In both cases, thefriction increased rapidly after a short period of operation (one hourin the case of these experiments) and very quickly became so great thatthe unit stopped running. In the case of curve III, the bearing waslubricated with lightweight oil of the kind used for oiling delicatemechanisms such as watches. After having started at a raised value, thetorque therein stabilized itself rapidly at a value of around 0.25g./cm. a value which is almost double than that measured for the casewhere no lubrication was used. However, the torque obtained with the useof the light oil remained constant during the entire duration of theexperiment, about 96 hours.

Finally, the curve IV shows the torque-time characteristic for the casewhere the bearing was lubricated by a substance representing oneembodiment of the present invention and consisting of the sphericalparticles suspended in alcohol. The starting torque for this test was inthe neighborhood of 0.08 g./cm., and, in proportion to the rate ofevaporation of the alcohol and to the rate at which the spheres spreadthemselves out uniformly between the lubricated surfaces, the torquediminished rapidly until the alcohol was completely evaporated, reachinga final value of 0.05 g./cm. The friction torque remained constant atthis value during the entire remaining period of the experiment.Comparison of the foregoing results clearly shows that the use of thelubricant of the present invention caused the friction torque to be fivetimes less than the value produced with the aid of the special lightoil, and that the lubricating quality of the spherical particles did notdiminish with time.

It should be noted at this point that the effectiveness of the novellubricants described above is augmented by an appropriate treatment ofthe surfaces between which they are to be used. Specifically, thesesurfaces should receive a finish which is of such a smoothness that thedeepest irregularities, be they lines or pits be less than one-third ofthe diameter of the spheres. 'Such a smoothness will insure that thespheres do not become rutted in these irregularities.

The desired polishing can be accomplished mechanical- 1y orelectrically, the technique used, of course, depending on the degree ofsmoothness required. In the case of mechanical polishing, it isnecessary that the helical or linear scorings which inevitably resultextend in many different directions and intersect each other irregularlyin order to prevent the movement of the spheres from being biassed inany particular direction or directions. In other words, the spheres rollat random.

The use of lubricants prepared according to the present invention offerssolutions to previously unsolved lubrication problems. For example, byapplying the spherical particles alone between two rubbing surfaces, oneobtains a lubrication which, for all practical purposes, is independentof variations in ambient temperature and pressure, and can thus be usedto lubricate materials which can themselves withstand extremeconditions. One example of such materials would be the new ceramicswhich withstand extreme temperatures.

The use of the spheres with such materials would be extremely valuablebecause these ceramics have the ability to withstand extremes oftemperature and pressure without changing their properties, and are,therefore, often used to replace metals under these conditions. However,these ceramics have the serious drawback of being incapable of engagingin sliding contact with one another without experiencing excessivefriction which tends to permanently damage them. The lubricants of thepresent invention are able to solve this problem because they possesslubrication properties which are as insensitive to temperature andpressure variations as are the ceramics.

Further, the use of the lubricants of the present invention simplifiesthe construction, the technology and the design of the surfaces ofceramic units because it permits the tolerances between pieces to bereduced to around 1 micron.

It is also possible to construct pillow blocks abutments and pivotscarrying cylindrical or frustoconical shafts or spindles turning inceramic housings which are lubricated by embodiments of the presentinvention, thus permitting the dimensions of the various parts to besuch that adjacent parts experience very little play, of the order of 1micron, for example.

Further, the employment of such narrow tolerances between moving partspermits the lubricated spaces to be highly impervious to theintroduction of foreign particles from the surroundings, and, to a largedegree, water tight and gas tight.

Turning to another field of application, it has been found that thelubricants of the present invention can be used to great advantage inthe textile, plastics and paper industries to remove certain sources ofstatic electricity, and thus reduce fire hazards. This result isachieved by using the spheres of the present invention, particularlythose made from iron or tungsten, as lubricants between the slidingsurfaces of machines thus taking advantage of the fact that theselubricants (which, when subjected to no pressure, act as dielectricshaving properties equivalent to those of mica), when subjected to even avery slight pressure, become electrical conductors which prevent theaccumulation of static electricity on any one part.

Those embodiments of the present invention which consist solely ofspherical particles could also solve many lubrication problems ofdevices designed to travel in outer space. In brief, the spheres, beingrelatively unaffected by either the extremely low temperatures andpressures of outer space or the extremely high temperatures experiencedby a device reentering the earths atmosphere, would provide aconsistent, effective lubrication during the entire period of flight ofsuch a unit.

Further, the lubricants of the present invention are insensitive toionized environments and hence would be very valuable lubricants fordevices working in such environments, such as in the nuclear industries.

The foregoing has represented an attempt to describe a few of thepossible uses for the lubricants of the present invention. It will beappreciated that the embodiments disclosed herein are capable of a greatmany variations, applications and modifications without departing fromthe spirit of this invention and it should, therefore, be understoodthat its scope is intended to be limited only by the breadth of theappended claims.

What is claimed is:

1. In combination with surfaces engaging each other slidably, alubricant between said surfaces comprising a plurality of calibratedspherical had particles having a diameter less than 40 microns, suchsurfaces having a polish sufficient to make possible the rolling atrandom therebetween of said spherical metallic particles.

2. A combination according to claim 1 wherein said particles are made ofa metal selected from the group consisting of iron, nickel, cobalt,aluminum, tungsten and bronze.

3. A combination according to claim 1 wherein said diameter is less thanabout 8 microns.

4. A combination according to claim 1 wherein said diameter at leastequals three times the deepest irregularities of said engaging surfaces.

5. A combination according to claim 1 wherein said slidably engagingsurfaces are made of ceramic.

6. A combination according to claim 1 wherein the diametral sizes ofsaid metallic spherical particles calibrated at a determined averagevalue D range within D D D and D+ 10 7. In combination with surfacesengaging each other slidably, a lubricant between said surfacesconsisting of a single layer of calibrated spherical hard particleshaving a diameter less than 40 microns, such surfaces having a polishsuflicient to make possible rolling at random therebetween of saidspherical particles.

8. In combination with surfaces engaging each other slidably, alubricant between said surfaces consisting of a nonvolatile organicliquid binder material containing therein calibrated spherical hardparticles having a diameter less than 40 microns, such surfaces having apolish sufiicient to make possible the rolling at random therebetween ofsaid spherical particles.

9. In a combination as claimed in claim 8, said binder material havinglubricating properties.

10. In a combination as claimed in claim 9, said binder material ismineral lubricating oil.

References Cited UNITED STATES PATENTS 2,021,885 11/1935 Bird 252l92,486,130 10/1949 Dietrich et al. 252-19 2,859,181 11/1958 Jordan et al.25219 3,007,867 11/1961 Allen et al. 25226 3,224,966 12/1965 Li252--12.2 2,697,028 12/1954 Baker et al. 23209.1

FOREIGN PATENTS 206,706 ll/1923 Great Britain 25226 OTHER REFERENCES TheMachinist, Mar. 13, 1954, pp. 433-411.

DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner U.S. Cl.X.R.

